Donald Trump's older sister Maryanne Trump Barry described the US president as a "cruel man" with "no principles" in a secret recording.
The tapes, published by the Washington Post, were secretly recorded by her niece Mary Trump in 2018 and 2019.
"All he wants to do is appeal to his base," Barry said. "He has no principles. None. None. And his base, I mean my god, if you were a religious person, you want to help people. Not do this."
In a statement provided by The White House by a spokesman, President Trump said the recordings were insignificant and dismissed the accusations.
"Everyday it's something else, who cares," Trump said. I'll continue to work hard for the American people. Not everyone agrees, but the results are obvious. Our country will soon be stronger than ever before!"
The recordings are the first time a family member, aside from his niece Mary Trump, has publicly criticised him.
"He was a brat!" Barry said about the president.
"The goddamned tweet and the lying, oh my god. I'm talking too freely, but you know."
"The change of stories. The lack of preparation. The lying - holy shit!"
Mary Trump told the Washington Post she recorded 15 hours of conversation between her and Barry in effort to back up some of the facts released in her recent book, 'Too Much and Never Enough: How My Family Created the World's Most Dangerous Man.'
Barry also alleged her brother asked someone to sit his SATs to enable him to get into university.
"I drove him around New York City to try to get him to college."
"I know he didn't get into college. And he - and he went to Fordham for one year and then he got into the University of Pennsylvania because he had someone take his - take the exams. SATs or whatever."